Circuit breaker for conductive-coated glass



Aug. 18, 0 M. E. S TRQMQUIST ET CIRCUIT BREAKER FOR CONDUCTIVE-COATEDGLASS Filed Feb. 16, 1968 14/0/05; 1/. ST/ZOMQU/ST James \r. HEQUEY I NVENTORS 4- oQJ Y US. Cl. 174-685 3 Claims ABSTRACT OF THE DISCLOSURE Asafety device for a refrigerator door containing a conductive-coatedtempered glass panel, in which the bus bar used to supply current to theconductive coating is frangibly bonded to the glass and arranged tosurround the edges of the glass completely to form a continuousbreakable current carrying barrier between the coating and the edges ofthe glass.

This invention relates in general to conductive-coated glass, and inparticular to safety devices for use with refrigerator doors employingsuch glass.

It has become common in modern day merchandizing to display foods whichnormally must be kept refrigerated, such as dairy products and meats.One preferred way of accomplishing such display is to place a product ina refrigerated compartment provided with a transparent door for removalof the product. Such a door usually consists of a metal frame enclosingtwo pieces of glass bonded together at their edges and separated by aninsulating air space.

'Experience has shown, however, that even in most arid regions the glassin this type of door is susceptible to being fogged up because of thedifferential cooling on the inside and outside of the door. One methodwhich has been used with considerable success to prevent this occurrenceis to coat the surface of the glass with a transparent conductivecoating and to pass electrical current through the coating to heat thesurface of the glass which is exposed to condensation. While this methodhas been generally satisfactory for the prevention of moisture formationon the glass surfaces, the conductive coatings themselves have posed apotentially serious safety hazard. Any separation in the conductivecoating, such as might be caused by thermal stresses within the glass orby percussive contact of the glass or the coating with an object, wouldresult in a high electric potential existing across the break and wouldpresent a danger of shock to anyone coming in contact therewith. Thisdanger can be minimized by utilizing low voltages rather than standardhouse current for heating the glass, but the expense of adapting theseinstallations to such voltages and installing the necessary transformersis prohibitive.

The present invention overcomes these disadvantages by providing aconductive-coated glass door having the bus bar supplying current to theconductive coating completely encircling the surfaces of the glass andadapted to be fracturedin the event the glass is broken. In case of sucha break the electrical voltage drop is across the break in the bus barand not in the region of the conductive coating. Since the bus bar iscovered by the frame holding the glass in the door, there is little ifany chance of a shopper coming in contact with the break. This chancemay be reduced still further by providing electrical insulation betweenthe frame and the glass and by sealing the frame to the glass so as toprevent moisture from seeping under the frame and contacting the break.

It is therefore the primary object of the present inven- 3,524,920Patented Aug. 18, 1970 tion to provide a new and improved safety devicefor refrigerated glass doors.

It is another object of the present invention to provide a safety devicefor glass doors having a conductive coating thereon.

It is a further object of the present invention to provide a safetydevice for conductive-coated glass surfaces to eliminate potential shockhazards therein.

It is still another object of the present invention to provide a new andimproved 'bus bar configuration for a conductive-coated glass door.

It is yet another object of the present invention to provide a new andimproved bus bar configuration for a conductive-coated glass door inwhich the bus has shears upon any fracture of the glass door.

These and other objects of the present invention will become moreapparent from the following detailed specification taken in conjunctionwith the accompanying drawings. It is to be understood however, that thespecification and drawings are for purposes of illustration only and arenot intended to be construed as a limitation upon the scope of theinvention. In the figures which follow, corresponding reference numeralsare carried forward whereever applicable.

FIG. 1 illustrates a typical conductively heated glass door installationfor a refrigerated storage and display case;

FIG. 2 illustrates a cross-section of FIG. 1 along 22;

FIG. 3 illustrates a bus bar layout according to the present inventionwith the two glass panels shown in FIG. 2 placed side-by-side fordiagrammatic purposes; and

FIG. 4 illustrates in greater detail the overlapping feature of the busbar arrangement of FIG. 3.

In FIG. 1, a portion of the front face of a refrigerated compartment isshown. This front face comprises a series of glass doors 11 comprisingglass panels 12 mounted in frames 13. The glass doors 11 are adapted tobe swung open to enable a purchaser to avail himself on the contents ofthe refrigerated compartment.

In FIG. 2, a section of one such door and its glass panels 12 andframing 13 is shown in more detail. As is illustrated, the framing 13 isadapted to receive therein a plurality of the glass panels 12 which aresealed thereto by means of sealant 14 and separated from one another bymeans of a spacer 15 which may be composed of an insulating substancesuch as polyurethane. In this configuration, the edges of glass panels12 are hermetically sealed with an air space between them to provide ahighly thermally insulated closure for the front of the refrigeratedcompartment.

As also shown in FIG. 2, a series of bus bars 16, 16' are fused to theinside surfaces of the glass panels 12 and serve to carry current to theconductive coating 17 formed on the inside surfaces of the glass panels12. The conductive coating 17 may beformed by the process of chemical orvacuum deposition and the thickness thereof is controlled so as to besubstantially transparent to light. In the forming process the coating17, like the bus bars 16, 16' actually becomes bonded to the glass. Asexplained previously, when electrical current is passed through the busbars 16, 16' and the conductive coating 17 the surfaces of the glasspanels 12 are heated sufficiently to prevent the condensation ofmoisture thereon.

FIG. 3 illustrates one embodiment of the unique bus bar configuration ofthe present invention which serves to prevent'the creation of anelectrical shock hazard when the conductive coating 17 is fractured dueto breakage of the 'glass panels 12 or either of them. As is seen inFIG. 3, the glass panel 12 has the conductive coating 17 depositedthereon and in electrical contact with bus bars 16,

3 16'. Electrical current is fed by means of leads 18 to the bus bars16, 16' and across the conductive coating 17. Since the conductivecoating 17 has a resistivity of the order of from 1 to 1000 ohms persquare, heat is generated uniformly across the entire coated surface ofthe glass panel 12.

As is illustrated in FIGS. 3 and 4, the bus bars of the presentinvention are fused to the glass panel 12 in a geometric configurationcompletely surrounding the panel 12. A critical feature of the subjectinvention resides in the laying out of the bus bars 16, 16 in a patternin which it is virtually impossible for any break in the glass panel tooccur extending to the perimeter of the glass panel 12 which would notalso result in a fracture through some portion of one or both of the busbars 16, 16'. At each position 19, 19' on the glass panel 12 where oneof bus bars 16, 16' ends, a portion of the other bus bar 16, 16' isfound to overlap the ended portion of the first bus bar 16, 16' so thatsubstantially no discontinuity of the bus bars 16, 16' exists withrespect to the outside perimeter of the glass panel 12. Thus since theheat tempered glass used in all present day glass refrigerated storageand display container doors always breaks to the outside perimeter ofsuch glass whenever any fracture of the glass occurs, and since the busbars 16, 16' of the present invention are fused to the surface of theglass panel 12, shearing of the one or both of the bus bars 16, 16 uponany fracture of the glass panel 12 is assured.

From this brief description it will be apparent that numerousmodifications may be made thereto without departing from the spirit andscope of the invention. For example, the subject invention readily maybe employed with a heated door in which the conductive coating isapplied to the surface of only one of the glass panels 12. In addition,the configuration of the bus bars 16, 16' shown in the regions 19 ofFIGS. 3 and 4 may be varied Cir as desired or required for any giveninstallation. The only requirement is that a portion one of the bus bars16, 16' must overlap the other bus bars free ends to form a continuousbreakable physical barrier between the central enclosed area of thepanel 12 covered by the conductive coating 17 and the panels edges.

What is claimed is:

1. In a conductively coated glass window unit, the

combination comprising:

a film of electrically conductive material bonded to the surface of saidglass so as to fracture therewith and spaced from the edges thereof; and

a pair of spaced bus bars bonded to said surface so as to fracturetherewith, one of said bus bars being in electrical contact with one ofthe edges of said film, the other of said bus bars being in electricalcontact with the opposite edge of said film, and each of said bus barshaving its ends overlapping and electrically insulated from the ends ofthe other of said bus bars.

2. The combination of claim 1, wherein said glass is heat tempered.

3. The combination of claim 1, wherein said glass unit is surrounded bya frame electrically insulated from, and completely covering said busbars.

References Cited UNITED STATES PATENTS 2,625,640 1/1953 Gaiser et al.219543 XR 2,954,454 7/1960 Gaiser 219-522 XR 3,263,063 7/1966 Marriottet al. 219522 DARRELL L. CLAY, Primary Examiner US. Cl. X.R.

Eli L11) UNIIM) S'I'AI'I'LS I'AI'I'ZN'I OFFICE (LMH'IIkICA'IE 0FCORRECTION Patent No. 3 524 920 Dated August 18, 1970 Inventor(s) M, E,fifIfBOMQUIST et a1 It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In the specification, in column 1, line 6, that portion of assignee'saddress reading "San Francisco, Calif should read -San Fernando,Calif.--.

SIGNED AND SEALED r um 27 1970 mm x. oomiflsioner of Petent Edward M.Fletcher, 11'.

Attesting Officer

